Imatinib is the current standard treatment for advanced GIST. Previous studies have shown that GIST genotype was associated with treatment outcomes with exon 11 having superior outcome compared with exon 9 or WT.10, 11 In patients with exon 9 kit mutation, the response rate was higher at when imatinib was given at 800mg daily compared with the standard dose of 400mg daily. Although the data linking tyrosine kinase mutation status and imatinib response in metastatic GISTs is intriguing, more information is needed before mutation testing is adopted as part of the routine analysis of high-risk or overtly malignant KIT-expressing GISTs.25 Despite the fact that exon 9 mutations are associated with a lower response rate, overall survival does not appear to be better with high-dose therapy. The investigators propose to conduct a retrospective analysis of mutational analysis on patients with GIST and determine the relationship between patient response and imatinib dose.